Optical projection apparatus



Jan. 10, 1928. 1,655,461

A. GRAVES OPTICAL PROJECTION APPARATUS Filed Feb. 18, 1925 2Sheets-Sheet l //VVE/V To 6 Filed Feb. 18, 1925 2 Sheets-Sheet 2//VI/E/V 7796 /,6 /YOL.D 666 Patented Jan. 10, 1928.

UNITED STATES ARNOLD GRAVES, OF LONDON, ENGLAND.

OPTICAL PROJECTION APPARATUS.

Application filed February 18, 1925, Serial No.

This invention refers to optical projection apparatus designed forprojecting an image or a message or a continuous succession of imagesor/and messages, or a plurality of separateimages or messages on to asurface or screen, whether transparent or opaque, for indicatingadvertising, shopwindow display or analogous purposes.

The said invention comprises the combination of a source of li ht toilluminate the object or image or the he (which it is desired toproject), with a concave reflector, in such a manner as to reproduceupon a screen or other surface an image of the object or image which ispositioned on the axial line of the reflector and illuminated in such amanner that rays of light emanate from the object or image and arereflected back past the object on to the screen or other surface wherethey come to a focus.

Thus, there is reproduced an enlarged, reduced or equal image of theoriginal object or image. These objects may be transparent or opaque andin any colour or plurality of colours. A mechanical device may also beemployed, whereby the object or image or series of objects or images ismoved horizontally or vertically or in some other manner across theaxial line, thus producing either an intermittent change of image uponthe screen or an effect of movement. This movement may be eitherintermittent or continuous and in the former case a synchronized shutteror some other system of temporarily obscuring the source of light or theilluminated object or image may be employed. A diaphragm or light shieldwith an aperture may be fitted, as being a simple method of obtainingsharpness of focus and minimum distortion, but the present invention isnot restricted to the employment of such a diaphragm.

In order that the saidinvention may be clearly understood, reference isdirected to the following description and accompanying drawings, wherein2-- Figure l is an elevation of one form of the apparatus with theprojecting screen (which is comparatively distant) omitted.

Figures 2 and 3 are diagrammatic plan and elevation respectively of analternative form. Referring to Figure 1, in this embodiment in which itis proposed to project a series or a continuous strip of translucentimages and/or objects, messages or the l ke,

10,055, and in Great Britainiebruary 18, 1924.

I employ a large concave reflector A, resting on a stand B which isfurnished with one fixed foot P and two adjustable feet 0 which permitof accurate levelling of the apparatus, a desirable but not essentialfeature. This reflector may be of the so-called Mangin type, or may havea polished reflecting surface formed by the revolution about its axis ofany one of the following curves, viz :the circle,the ellipse, theparabola, the hyperbole, or of modifications of such curves. PreferablyI employ either a Mangin or a hyperbolic type as giving the truest imagewithout much distortion. In front of this reflector and along the axialline thereof is mounted a cylindrical carrier F having its axis in avertical plane.

To the top of or above this cylinder is fitted or attached a horizontalpropeller D, consisting of a series of inclined blades or vanes whichspin freely on the needle supported by the carrier L and carry lugswhich support the cylindrical carrier F, which carries the revolvingskirt G of transparent material on which is printed, drawn, painted,written or attached the objects, messages or images to be projected. Thepropeller D tends to revolve the cylinder F about its axis when aircurrents pass up and impinge on the blades D. The cylindrical carrierwith its object skirt G more or less encloses an electric light bulb orother source of light C, which can thus function. in the dual role ofsource of light and source of heat for providing by convection theupward air cur rents which cause the cylinder to revolve.

As stated, the objects or images are mounted on the carrier in sequencein the form of the skirt G below the carrier, or the carrier may belengthened vertically and the objects mounted across apertures or slotscut in the carrier F itself. The height of the carrier in relation toits enclosed light source is adjusted so that the mass of the light isin the same horizontal plane as the images and the construction ismounted in such a mannor that the centre of the image is along thecentral axis of the reflector, and at a distance from this reflectorthat varies in accordance with the distance of the screen or surface onto which the image will be rojected. Mechanical means for varying tiieseadjustments-may be fitted if desired. For instance, as shown, a bracketK is mounted in front of the reflector and provides adjustment in threedirections, namely, outwards,

upwards and sideways, for the fittings mounted thereon.

The objects may be of or on opaque material illuminated by the lightsource C reflected on to the projecting-reflector A, and thence to thescreen. In this case, the li ht distribution may be arranged so as tofall on to the outer surface of the band G directly facing the mirrorwhere it is required to project images of opaque subjects, etc.

An aperture or diaphragm H may be employed to diminish astigmatism andaberrations produced by the marginal rays. i/Vhen used, this aperture ispreferably mounted where the light rays converge between the imagecarrier and the screen. This diaphragm H, consisting of a flanged discwlth a central circular aperture, is mounted in front of the apparatuson a support Q.

It is desirable, although not essential, to mask all rays of light fromthe light source other than those impinging on the object or image to beprojected. This may be done by encasing the light source with alightproof material in which a slot is cut through which the li ht isdirected on to the object or image. 11 the case of an electric lightbulb, this may also be done by coating the outer surface with alight-proof paint or other substance, leaving a slot exposed betweemthefilament and the object or image in position for projection. Thiselectric lamp may be replaced by a gas or oil burning light source tosuit expediency.

Above the revolving vanes D a damper or brake N is suspended from itssupporting carrier M, and the speed of the revolving mechanism can becontrolled at will by adjusting the height of the brake in relation tothe vanes.

The employment of the above means of obtaining movement by theconversion of radiant energy into kinetic energy is known and is not anessential feature of this invention, although it will be employed in oneembodiment thereof. Other means, such as clockwork, electric motors, orsolenoids, and other known means can obviously be employed. Again, theaxis of the rotating carrier may be positioned in positions other thanthe vertical, according to the motive power employed.

It is understood that a plurality of light and/or heat sources may beemployed and will come within the scope of this invention. Further, therotating carrier need not be cylindrical but might be of any shapeprovided that the objects or images are consecutively presented to thereflector in the same position and alignment.

In other embodiments of this invention a variety of mechanical means anddevices may be employed to bring the objects or images into position forprojection, or even single objects may be presented. .Or the apparatusmay be combined with existing combinations of mirrors, prisms and soforth interposed between the projector and the screen or otherprojection surface. Or again a. screen may be utilized embodying otherimages or devices, or a known type of translucent screen employed whichhas a reflecting mirror surface.

It is clear that all such devices are accessorics and that apparatusembodying them into the main principles come under the scope of theinvention.

Illusions and distortion effects may be obtained by altering theposition of the surface upon which the images are projected or byprojecting on to irregular or multiple surfaces or by imparting movementto this surface, or by applying the same principles to the objects orimages to be projected, or by employing reflectors which produce effectsof distortion.

Figures 2 and 3 show an embodiment of this invention in which A is aconcave reflector resting on a stand B. Four rollers F, F, F Frespectively are mounted on suitable supports in such a manner that anendless band G, on which the messages, objects, or images are printed,drawn, painted, written or attached, passes horizontally across a pointin front of the centre of the reflector and at such a distance from itthat the projected rays come to a focus on the screen S. At the side ofthis band G furthest from the reflector is mounted an electric lightbulb C, the majority of whose surface is obscured or screenedexteriorly, leaving a small aperture or window exposed to illuminate theportion of the band directly opposite the centre of the reflector. Anelectric motor D, by means of a reduction gear and a driving spindle E,or some other suitable mechanism, causes the drivin roller l5 to revolveat the required spee thus causing the band G with its images, etc., topass across the focal centre of the reflector A which reproduces asimilar movement of the image produced on the screen at S. An eventension is maintained on the band G by a tension or jockey roller F .orsome other similar system. It is obvious that the position or number ofthe rollers is variable and that these may even be replaced by othersuitable mechanism. Again, the movement of the images need notnecessarily be horizontal since, by turning the apparatus on its side,the movement immediately becomes vertical. A diaphragm H may be fittedif desired, and is preferably mounted, as shown, in front of theapparatus. This diaphragm consists of a sheet of metal or wood or othersuitable material, with a circular aperture whose centre is in theoptical axis of the system. A rectangular screen S of ground glass orsome other suitable translucent or opaque material receives the messageor image projected.

When a diaphragm is employed, a tunnel effect is produced which greatlyenhances the brilliancy of the image.

For mobile messages'or image display on motor vehicles, trains, boatsand the like lamps and other driving gear may be fitted that will besuitable for employment with the existing electrical equipment of thevehicle in question, and the embodiment shown in this diagram isapplicable to this special form of publicity, but is obviouslyapplicable for other purposes, including PIOJEC- shortening the distancebetween the lens and the screen, orfor varying their relative positions.

I claim A picture projecting apparatus compris ing a lamp having oneside portion transparent and the opposite side impervious to thepenetration of light, a concave reflector facing the transparent portionof the lamp and spaced therefrom, means for moving a translucent picturebetween the transparent portion of the lamp and said reflector, and ascreen disposed opposite the light impervious portion of the lamp andspaced therefrom and adapted to intercept rays of light emanating fromthe lamp, also those penetrating the picture, and those reflected fromthe reflecting surface.

In testimony whereof I have aflixed my signature hereto this third dayof February, 1925. ARNOLD GRAVES.

